The conductive parts to be used in an electronic or electric device are represented by a lead frame which is used in a semiconductor unit such as a transistor, an IC, an LSI (i.e., Large Scale Integration), an SCR (i.e., Silicon Controlled Rectifier: a thyristor). This lead frame is mounted in the IC or semiconductor element by a process having the following steps.
First of all, a strip of a conductive material having a thickness of 0.1 to 0.5 mm is prepared as the material for the lead frame. This strip is pressed or etched into a desired lead frame shape (having its outer leads united). Then, a semiconductor element (e.g., a Si (silicon) chip) made of highly pure Si is bonded to a predetermined portion of that lead frame. This is called the "die-bonding" step, which is exemplified by: the press bonding using a conductive resin such as Ag (silver) paste; the method of bonding the lead frame and the semiconductor element by preforming a plating layer composed of one lamina or two or more laminas of Au (gold), Ag or Ni (nickel) and by thermally diffusing and bonding through that plating layer to form an eutectic of Au - Si; or the bonding method using solder of Pb (lead) - Sn (tin). After this, the Al (aluminum) electrodes over the semiconductor element (e.g., Si chip) bonded to the predetermined portion of the lead frame mounted on the substrate are connected to the conductor terminals (i.e., inner leads) of the lead frame through Au or Al wires. Subsequently, the semiconductor element, the connecting portions and the lead frame, in which the semiconductor element is mounted, are sealed with a resin or ceramics so that they may be protected. At last, the mutually united portions of the outer leads of the lead frame are cut away.
The lead frame material to be manufactured by the process described above is required to have an excellent pressability or etchability; excellent heat (or softening) resistance, platability and solderability at the step of die-bonding the semiconductor chip (e.g., Si chip) and the lead frame; excellent radiatability (or thermal conductivity) and electric conductivity; strength and ductility sufficient for being free from any breakage even if the semiconductor device is bent one or many times when it is to be transported or mounted in an electric device; and corrosion resistance.
The lead frame materials used in the prior art are the 42 alloy of Fe (iron) - Ni (42 %); the alloy of Fe - Co (cobalt) (17 %) - Ni (29 %), which is known under the trade name of "Koval"; phosphor bronze (e.g., CA 501) of Cu (copper) system alloy; Cu - Fe - Zn (zinc) - P (phosphor) alloy (e.g., CA194); Cu - Fe - Co - Sn - P alloy (e.g., CA 195); and so on.
Of the above-enumerated lead frame materials, however, both the Koval and the 42 alloy contain large percentages of expensive Ni so that they have to become expensive, whereas the Cu system alloys are inferior in the bending repeatability and are troubled in their production costs. It is, therefore, earnestly desired for the conductive material for the conductive parts of an electronic or electric device and represented by the lead frame material to satisfy the several properties required thereof and to be developed and practiced at reasonable costs.
Generally speaking, aluminum alloys are known as the conductive materials produced at reasonable costs. In the prior art, however, the aluminum alloys are accepted not to sufficiently meet the aforementioned several properties required of the lead frame and so on. Thus, the fact is that the lead frame materials of the aluminum alloys are not practically used.
The present invention has been conceived in view of the background described above and has an object to provide a material for conductive parts of an electronic or electric device, which is made of an inexpensive aluminum-based alloy and which has excellent softening resistance, electric conductivity, thermal conductivity (or radiatability), solderability and platability, high mechanical strength, and excellent bending repeatability.